Hematite

The streak test is the heart of any hematite identification and almost never fails. Rub the specimen on an unglazed porcelain tile: hematite leaves a rusty red to red-brown streak even when the mineral itself looks silvery-gray or black. This single test separates hematite from nearly every metallic look-alike, most of which streak gray or black.

After the streak, weight and hardness narrow it down. Hematite is dense and feels heavy in the hand, and it is moderately hard (5–6.5) — hard enough to scratch glass in its compact forms, though crumbly earthy hematite can feel much softer because the grains rub loose. It is opaque in all forms, so no light passes through.

Magnetism is a useful confirming test. Unlike magnetite, natural hematite is at most weakly attracted to a strong magnet and usually shows no obvious pull at all. If a metallic, red-streaking specimen is strongly magnetic, suspect magnetite (or a man-made magnetic material) rather than pure hematite.

Hematite is unusually varied in appearance, which is the main reason beginners misjudge it. The same mineral can look like a polished mirror or like dried red mud, so it helps to learn its named forms.

Specular hematite (specularite) is the flashy variety: silvery to steel-gray, with a bright metallic, almost mirror-like sheen, often made of countless tiny sparkling platelets. Polished black hematite jewelry comes from this dense, metallic material.

Kidney ore (botryoidal hematite) forms smooth, bulging, rounded masses that look like clustered kidneys or bunches of grapes, typically dark gray to reddish with a metallic-to-silky surface and a radiating fibrous interior when broken. Earthy or "red ochre" hematite, by contrast, is dull, soft and brick-red to red-brown, and it readily stains your fingers — this is the pigment form used in paints and dyes. Hematite also occurs as thin red coatings that color sandstone, quartz and many other rocks red. Whatever the outward form, the red streak ties them all together as one mineral.

Hematite forms wherever iron meets oxygen, which makes it one of the most widespread minerals on the planet. It precipitates from iron-rich waters, crystallizes from hot hydrothermal fluids, forms as iron-bearing minerals weather and rust at the surface, and occurs as a pigment dispersed through sedimentary rocks. Its red iron-oxide stain is responsible for the color of red sandstones, red soils and many desert landscapes.

On a vast scale, hematite is a major component of banded iron formations — ancient layered rocks that record a time when oxygen first built up in Earth's oceans, and which today make up the world's largest iron-ore deposits. It is commonly found with quartz, magnetite and other iron minerals, and the same mineral lends Mars much of its rusty-red color, earning Earth's hematite a place in planetary science as well.

In crystal and metaphysical traditions, hematite's heavy, metallic feel has made it a popular "grounding" and protective stone, often associated with stability, focus and absorbing stress. These ideas are cultural and spiritual rather than scientifically established medical effects, and hematite is not a substitute for medical care — magnetic-hematite bracelets in particular are marketed with health claims that are not medically proven (and most are synthetic material, not natural hematite).

Practically, hematite's importance is industrial: it is the world's principal ore of iron and the raw material behind most of the steel around us. In powdered form it is a classic pigment (red ochre and "rouge"), used in paints, polishing compounds and, historically, in cosmetics and cave art. Polished specular hematite is also cut into beads, cabochons and the dark, mirror-bright jewelry sold simply as "hematite."

Hematite is abundant and inexpensive. As a collector's mineral, value comes from form and quality rather than rarity: bright, well-crystallized specular hematite, attractive botryoidal kidney ore, and the rare rosette clusters known as "iron roses" are the most sought-after, while common earthy red masses are worth very little. Polished jewelry pieces are priced for their luster and finish.

Hematite is reasonably hard and chemically stable, so it does not suffer the decay that plagues pyrite. It can be cleaned with water and a soft cloth, but earthy varieties will shed red powder and stain, and the metallic polish on jewelry can be dulled by abrasion or scratched by harder stones. Synthetic magnetic "hematite" is a different, man-made product; if magnetism matters to you, test before you buy, since genuine hematite is at most weakly magnetic.